Objectives: (a) To develop a broad knowledge of intrauterine and transplacental virus infections, based on actual work with a number of agents. (b) To create animal models, first of Down's Syndrome and second of open neural tube defects such as exencephaly, both of which are important in human terms and both of which, I feel, are viral in origin. (c) To show ultimately that knowledge built up in these projects does have relevance to the problem of human cancer. Methods: Will be those worked out in 14 previous publications on Transplacental Viral infections, all dealing with pregnant hamsters, rats, and mice, with virus isolations in tissue cultures and close cooperative studies in histopathology and immunofluorescence. Brief abstracts of projects: (1) Study of transplacental infections in Pregnant Hamsters due to Reovirus Type III and of the synergism between the virus and a congenital myopathy. (2) Study of mumps virus infections in pregnant and fetal hamsters as well as of new findings induced in CNS of neonatal hamsters. (3) Long term effort to induce odontogenic tumors in Multimammate Mice with Minute Virus of Mice (MVM). (4) Effort to produce an animal model of Down's Disease in Hamsters, starting with MVM. (5) Studies of Karyotypes of defective newborn piglets on pig farm to confirm abnormalities already encountered. (6) Efforts to isolate virus or discover etiology of a spontaneous hemorrhagic necrocis encountered in brains of fetal hamsters. (7) Continued efforts to find virus cause of exencephaly and spina bifida found spontaneously in mice and hamsters and seemingly passed on two occasions.